Patent Application
20130302609
The present invention relates to a hydrophilic composition for use with a lubricating system and to an apparatus and a method using the same to remove water or other hydrophilic materials from the lubricating system.
US 2005/0197260 discloses an environmentally-friendly grease composition comprising a vegetable oil and a cellulose fiber, as well as also glycerin, a rust inhibitor and/or fatty acid ester, lecithin and/or phophatidyl choline.
U.S. Pat. No. 6,482,780 discloses a grease composition for a roller bearing comprising a metal soap-based thickening agent containing a long fiber-like material having a major axis length of at least 3 microns incorporated in a base oil comprising a lubricant having a polar group in its molecular structure and a non-polar lubricant blended in combination.
U.S. Pat. No. 5,874,391 discloses a polymer-thickened grease that is prepared by mixing a polymer, such as polypropylene, with a base oil and heating the mixture to fully dissolve the polymer in the base oil. The heated mixture is then rapidly cooled or quenched.
U.S. Pat. No. 5,415,791 discloses a lubricating composition for solid lubricant-embedded sliding members comprising 5 to 78% by weight of a solid lubricant powder material, 5 to 30% by weight of a lubricating oil which is in a liquid or paste form at ordinary temperatures, 1 to 15% by weight of a carrier for absorbing and retaining said lubricating oil, and 15 to 50% by weight of a thermosetting synthetic resin binder. The carrier may be an oleophilic fiber, such as cellulose fiber and polypropylene fiber.
The performance of known lubricating systems is negatively affected when water or other hydrophilic materials (fluids) are undesirably introduced into the system during the operation of a device that is being lubricated by the lubricating system. Such undesirable aqueous materials can reduce the service life of the lubricant and/or can cause corrosion of the device. Previous solutions for removing and/or eliminating water or other hydrophilic materials from the lubricating system have been inadequate.
It is therefore an object of the present teachings to disclose an improved hydrophilic composition for use with a lubricating system, an apparatus utilizing the hydrophilic composition and a method for removing water or other hydrophilic materials from a lubricating system.
This object is achieved by the inventions of claims 1, 20, and 23, respectively.
Further developments of the invention are recited in the dependent claims.
According to a first aspect of the present teachings, a hydrophilic composition is disclosed for use with a lubricating system and comprises hydrophilic fibers having a diameter between 50 nm and 10 microns and a length that is at least 5 times the diameter. The hydrophilic fibers have a strong affinity for water and/or other hydrophilic fluids in the lubricating system, which preferably comprises oil and/or other lubricating fluid(s), e.g., hydrophobic fluids and/or substances, such as grease.
Such hydrophilic (preferably hygroscopic) fibers are capable of advantageously eliminating, removing or absorbing any free water and/or any dissolved water in the lubrication system, thereby improving the lubricating performance of the lubricating system, increasing the service life of the lubricating system and/or reducing corrosion problems of the parts in need of lubrication.
In another aspect of the present teachings, the hydrophilic fibers may be disposed on, adhered to, and/or embedded/incorporated into a system and/or machine in need of lubrication, e.g., on a surface thereof that is in fluid communication with the oil or other lubricating fluid. Such hydrophilic fibers may be advantageously utilized in bearing devices and/or other devices that include or contain oil or other lubricating fluid(s) as a component of a lubricant system. The devices may include a sealed portion containing the oil or other lubricating fluid(s).
In addition or in the alternative, the hydrophilic fibers according to the present teachings may be disposed in fluid communication with, e.g., in proximity to, a surface in need of lubrication. In this case, an oil or other base lubricating fluid may then be brought into contact with hydrophilic fibers, whereby water and/or other hydrophilic compositions in the lubricating system may be removed or absorbed by the hydrophilic fibers.
In addition or in the alternative, the hydrophilic fibers may be provided in the form of a fabric material, such as a non-woven pad, mat or cloth. The fabric material may be affixed to or embedded in a surface that is exposed to, i.e. is in fluid communication with, the lubricant, but preferably spaced away from the surface that is in need of lubrication. Again, by allowing the oil or other base lubricating fluid to contact the hydrophilic surface/fabric material, water and/or other hydrophilic substances can be effectively removed from the lubricant.
Since the hydrophilic fibers can be produced from a wide range of materials, the present teachings advantageously enable a wide flexibility or choice in the selection of the hydrophilic (fiber or fibrous) material.
As utilized in the present teachings, the term “hydrophilic” means that the surface of a flat piece of the material (i.e. the material that will be used to form the hydrophilic fibers or fibrous material) will be readily covered (wetted) by water, because that will reduce the total surface energy of the system. The more hydrophilic the material is, the smaller the “contact angle” of the drop of water on a flat smooth surface of such material will be, which makes the contact angle a suitable measure of the degree of hydrophilicity in accordance with the present teachings. In principle, if a small drop of water exhibits an inner contact angle that is less 90 degrees when dropped onto a material, such material can be considered hydrophilic. A higher degree of hydrophilicity of the hydrophilic fibrous materials according to the present teachings (i.e. a smaller contact angle) may be more advantageous in certain embodiments.
Similarly, as utilized in the present teachings, the term “oleophilic” means that the surface of a flat piece of the material (i.e. the material that will be used to form the oleophilic fibers or fibrous material) will be readily covered (wetted) by oil or another base lubricating fluid, because that will reduce the total surface energy of the system. A porous structure of an oleophilic material will absorb oil, like a sponge, through capillary action. The more oleophilic the material is, the smaller the “contact angle” of the drop of oil on a flat smooth surface of such material will be, which makes the contact angle a suitable measure of the degree of oleophilicity in accordance with the present teachings. In principle, if a small drop of oil exhibits an inner contact angle that is less 90 degrees when dropped onto a material, such material can be considered oleophilic. A higher degree of oleophilicity of the oleophilic fibrous materials according to the present teachings (i.e. a smaller contact angle) may be more advantageous in certain embodiments.
The sole FIGURE shows non-limiting examples of possible locations for arranging one or more water-absorbing structures in a roller bearing.
As an initial matter, it is noted that hydrophilic fibers according to the present teachings may be utilized with a wide variety of fluids, e.g., oils or other base lubricating fluids, that exhibit lubricating properties at the operating temperatures appropriate for various applications.
Particularly suitable lubricants (oils) include, but are not limited to, mineral oils obtained from crude oil, group I, II and III lubricants, group IV lubricants (polyalphaolefins “PAO”) and group V lubricants (all others).
A more particular, but non-limiting, list of lubricating oils includes mineral oils, synthetic esters, and plant-based oils and their derivatives, such as oils derived from rapeseed, canola, sunflower, canola, and palm. Animal-based oils, their derivatives and synthetic lubricants also may be suitably used in certain aspects of the present teaching including, but not limited to, polyglycols (PG), polyalkylene glycol (PAG), white oils, silicone oils, very-high viscosity index oils (VHVI), water, glycerol and waxes.
Particularly preferred oils according to the present teachings are mineral oils, synthetic esters, PAOs and synthetic hydrocarbons.
The viscosity of the lubricating fluid (oil) can range from very low (below 1 cSt at 40° C.) to very high (several 1000 cSt at 40° C.). The most suitable viscosity depends on the application temperature, operating (e.g., rotating) speed, etc., and the present teachings provide for a wide variety of possible lubricating properties. However, particularly preferred are any of the above oil types that have a viscosity between 10 and 300 cSt at 40° C.
In principle, the hydrophilic (and/or oleophilic) fibers according to the present teachings can be made, e.g., from any type of polymeric materials that can be spun into fibers, as well as in conjunction with optional additives. Suitable polymers include, but are not limited to, polyamide (PA), nylon 6,6, polyamide-6,6 (PA-6,6), polyamide-4,6 (PA-4,6), polyurethanes (PU), polybenzimidazole (PBI), polycarbonate (PC), polyacrylinitrile (PAN), acrylonitrile rubber (NBR), polyvinylalcohol (PVA), polylactic acid (PLA), polyethylene-co-vinyl-acetate (PEVA), polymethacryate (PMMA), tetrahydroperfluorooctylacrylate (TAN), polyethylene oxide (PEO), collagen-PEO, polyaniline (PANI), polystyrene (PS), silk-like polymer with fibronectin functionality, polyvinylcarbazole, polyethylene terephtalate (PET), polyacrylic acid (PAA), polypyrene methanol (PM), polyvinylphenol (PVP), polyvinylchloride (PVC), cellulose acetate (CA), polyacrylamide (PAA), poly(lactic-co-glycolic acid) (PLGA), collagen, polycaprolactone (PCL), poly(2-hydroxyethyl methacrylate) (HEMA), poly(vinylidene fluoride) (PVDF), polyether imide (PEI), polyethylene glycol (PEG), poly(ferrocenyldimethylsilane) (PFDMS), poly(ethylene-co-vinyl alcohol), polyvinyl pyrrolidone (PVP), polymetha-phenylene isophthalamide, polypropylene (PP), polyethylene naphthalate (PEN), Teflon®, polytetrafluorethene (PTFE), waxes, waxy polymers, polyolefins, polyesters, polysulfones and polyether sulfones (PES).
Polymers that are intrinsically hydrophilic can be used without further treatment. Polymers that are not hydrophilic can be rendered hydrophilic (hygroscopic) by either a chemical or physical post treatment, or by the adsorption of amphiphilic species on their surface. Intrinsically hydrophilic fibers can be rendered more hydrophilic by similar post-treatment in order to adjust the hydrophilicity and/or hygroscopicity to a desired level for a particular lubricant and/or application of the present teachings.
Examples of intrinsically hydrophilic polymers include, but are not limited to, acrylamides, such as polyacrylamide, acrylates, such as polyacrylic acid, maleic anhydride copolymers, methacrylate, ethyl acrylate, amine-functional polymers, such as polyallylamine, ethyleneimine, oxazoline, and other polymers containing amine groups in their main- or side-chains, ethers, styrenes, such as polystyrenesulfonate and related polymers, vinyl acids, and vinyl alcohols, such as polyvinyl alcohol. An example of a polar, but water-insoluble polymer is poly(vinylpyridine).
Preferred are polymers or their versions that, under application/usage conditions, will attract water and/or other hydrophilic substances and absorb it (them) into its fibrous network, such that the water and/or other hydrophilic substances are not allowed to dissolve or be released back into the lubricating fluid.
PP and PA are also preferred and may be suitably modified to be hydrophilic by appropriate post treatments.
In addition or in the alternative, polymers derived from natural or biodegradable sources are also suitable for making fibers that can be utilized with the present teachings. An added benefit is that many of such polymers are intrinsically hydrophilic and may not require any further post-treatment to render them sufficiently hydrophilic and/or hygroscopic for purposes of the present teachings. Representative examples of such polymers include, but are not limited to, polysaccharides, such as cellulose, starch, chitin, chitosan, proteins, (poly)peptides and gelatin.
Of course, mixtures or blends of two or more of the above-noted polymers are suitable as well. All possible combinations of two or more of the above-mentioned polymers are understood as being expressly enumerated for the purposes of original description.
In one embodiment of the present teachings, a small fraction (e.g., 0.1-5%) of fibers of one type can be added to grease that primarily contains a second type of fiber so as to impart special properties to the grease. For example, the fibers can be designed to melt at elevated temperatures to form a lubricant. In addition or in the alternative, the fibers can contain additives. In addition or in the alternative, the fibers can provide a structural function in the lubricant or grease.
Mixtures of two types of fibers A and B in a ratio A:B between 10:90 and 50:50 can be utilized to impart unique properties to a hydrophilic (e.g., hygroscopic) fibrous network.
The hydrophilic fibers can be between 0.1 and 100 wt % of the final material. More preferably, a hydrophilic material according to the present teachings preferably contains 50-100 wt % of hydrophilic fibers and may be in the form of a pad or fabric made of the fibers, which may be affixed at a location within the lubrication system and in fluid communication with the lubricating fluid.
In another preferred aspect of the present teachings, a micro/nano fiber network can be prepared from oleophilic fibers that will naturally embed, incorporate or absorb oil or another suitable base lubricating fluid, such that the overall process for making the lubricant is simplified to a great extent. Oleophilic fibers can be made from a variety of different materials, as mentioned above, and the length/diameter ratio of the fibers, as well as the chemical composition (bulk or surface) thereof, can be tuned or suitably selected, as was mentioned above, using a variety of different existing processes that are inherently low cost in nature. The construction of a soap-like or sponge-like structure by forming a cloth, pad, fabric, mat or sponge-like network from the oleophilic fibers described herein, or by appropriately dispersing the fibers in an appropriate lubricant, is also possible.
In another aspect of the present teachings, a cloth, pad, fabric or mat material can be produced from a variety of different polymer materials, such as the fiber materials mentioned above. The cloth, pad, fabric or mat material may be hydrophilic (e.g., hygroscopic) or oleophilic depending upon the polymers utilized and any post-fabrication treatment performed to change the properties of the cloth, pad, fabric or mat material.
In one exemplary example of the present teachings, an oleophilic fabric or pad material may be disposed at or proximal to a point of contact (e.g., a sliding surface) in need of lubrication to locally form a thickened lubricant, e.g., grease or a grease-like substance, at the point of contact by contacting the lubricating fluid (e.g., oil) within the lubrication system. In addition, a hydrophilic fabric or pad material may be disposed at a location spaced from the point of contact (i.e. a location within the lubrication system that does not require lubrication during operation), but in fluid communication with the lubrication fluid, so as to remove any water or other hydrophilic substances in the oil or lubricating fluid within the lubrication system.
In addition, the pad or fabric material may also be made with suitable lubrication additives included within or in the surface of the fibrous network, e.g., a non-woven fibrous network. This provides flexibility in producing unique, low weight structures that will only require placement in a convenient location within a lubrication system, followed by the addition of an oil or another base lubricating fluid. The properties of the fibers can be tuned or suitably selected or treated in order to adjust the physical properties (e.g., length, diameter, mixture, etc.) and/or the chemical properties (surface treatment, bulk material, wetting behavior, etc.), which selection and/or treatment will enable the fibers to be suitably adapted to any type of lubricating fluid.
In other embodiments, the fibers can be cut to a specific length and thus the fibers can be utilized in a loose or dispersable state. In another method for preparing fibers of a shorter length then has been available in the past, a cloth or fabric made of the fibers may be frozen and then the polymeric fibers are crushed while they are in a brittle state.
Such non-woven fiber fabrics mats can be made, e.g., by melt blowing micron or sub-micron diameter fibers, or by electro-spinning In addition, fiber material mats/cloths that may be advantageously utilized with the present teachings can also be obtained from commercial sources, such as Hills Inc. of W. Melbourne, Fla., U.S.A.
The fiber network may be organic and/or inorganic. The fiber fabrication method may be made compatible with a very large volume production.
The diameter of the fibers is preferably in the micron or nanometer range, while the length of the fibers is preferably in the range of several to tens of microns, most preferably less than 30 microns (μm). Preferably, nanoparticle materials (i.e. nanometer-sized particles having a low aspect ratio, e.g., about 1) that could present health hazards, which would limit their application, may be avoided.
The fiber diameters are between 50 nm and 10 microns, more preferably between 100 nm and 1 micron. Further, the fibers have a length that is at least 5-10 times the diameter thereof. That is, the fibers preferably have an aspect ratio of at least 5 to 10. The length of the fibers can be suitably modified to effect desirable changes to the structural properties thereof, its mechanical stability, and its bulk hygroscopic properties. Thus, the fiber length can be optimized for particular application (usage) conditions.
The base material for the fibers can be produced and tuned/adapted for a specific application. For example, the base material can also be sent to a final user as a cloth/fabric material or a network of pre-cut fibers. In this case, the final user would only need to add oil, lubricating fluid or grease to produce the lubricant system with water absorption capability. This aspect of the present teachings provides a great degree of flexibility, because the base material can be shipped worldwide relatively inexpensively, due to its low weight (i.e. unlike oil or greases, which are relatively heavy).
The hydrophilic fibers, any fabric or network-like materials made from the fibers, the lubricant fluid/oil and/or the thickened lubricant (e.g., grease) according to the present teachings may include one or more known additives that are commonly used in the lubricant field. The additives may be included to give the lubricant special functionality with respect to the aging of the lubricant (e.g., anti-oxidants), friction reducers, anti-wear, extreme pressure properties, etc.
Additives can also be added to give the lubricant or grease a stronger structure by linking or connecting (e.g., bonding) the fibers using suitable polymers, waxes or the like. Fibers having different properties can be used as additives as well.
Other suitable additives include ceramic particulates (silica, aluminia, zirconia, etc) and metallic particles.
The additives can be added to the polymer bulk base before the fibers are produced, but could also be added to the dry fibers. Small quantities of a carrier fluid (very suitable is a lubricant with or without additive) can also be added to the dry polymer base material. The oil or lubricating fluid then can be subsequently added to make the final formulation.
The additive(s) can also be added to the oil, which is then contacted with the fibers or fibrous material (e.g., the cloth/fabric made from the fibers).
In another aspect of the present teachings, the fibers themselves may serve as an additive. For example, the fibers disclosed herein may be added to known lubricants (e.g., oil, greases and emulsions) to improve the lubrication and hygroscopic performance thereof.
In another aspect of the present teachings, different materials or material properties can be mixed or combined in the same fiber, thereby achieving a phase separation and heterogeneous fibers. Consequently, a differentiated or dual behavior can be achieved in a single fiber. Such multi-property or multi-phase fibers may be referred to as a “JANUS fiber” after the Greek god who had two faces. Such multi-property or multi-phase fibers are highly advantageous to the development of mechanical stability (when needed) and to the ability of the hydrophilic material to self heal. That is, after some type of disruptive mechanical action (e.g. shearing), the fiber structure may preferably heal itself (e.g., self re-assembly) once again into the desired structure (network).
The Janus fibers can be produced according to a variety of methods. For example, the fibers can be subjected to a spray treatment, a plasma treatment and/or deposition process that exposes the fiber on one side. A deposition material can be a metal, polymer, small ceramic, metallic or organic nano-particulates that is/are embedded into or attached to the fiber on one side, e.g., the exposed side. This can be done either during the production of the fibers or after the production thereof. The deposition will create fibers with different properties on the exposed and the unexposed sides. Another way is to prepare two different types of polymers in parallel and then form them into one single fiber using existing micro-scale extrusion techniques. These are sometimes referred to as Island-In-Sea fibers in which a plurality of nano or micron-scale (bi-component) fibers are extruded in a matrix of a third polymer.
Another aspect of the present teachings relates to improve lubrication systems, e.g., for bearings, linear actuators, gears and any other mechanical raceway, track or sliding surface.
For example, in this aspect, hydrophilic fibers of the present teachings can be disposed, e.g., adhered onto or embedded/incorporated into a surface, so as to be in fluid communication with a sliding surface of a device, such as the raceway of a bearing, a gear or a linear device (motor), in order to form a deposit of the fibers that will provide a water removal function for the lubricating fluid (e.g., oil) that comes into contact with the deposit of fibers. However, the hydrophilic fibers are preferably not disposed at a point of contact/friction within the device in need of lubrication, so as minimize the likelihood that any water, which has been absorbed by the hydrophilic material, is released back into the lubricating fluid due to the high pressure and/or temperature conditions existing at the point of contact (i.e. the surface in need of lubrication during operation of the device).
The fibers can also be applied as a preservative measure in order to provide a better long term storage resistance of the mechanical components. This feature of the present teachings provides a desiccating function in an oil-lubricated system (e.g., such as an industrial gearbox). Because the effect is achieved in-situ, it leads to longer service life and local elimination of water and/or other hydrophilic substances from the lubricating fluid.
Various embodiments, features and advantages of the present teachings will now be described in more detail in the following.
Melt-spinnable fibers can have very different chemical properties. For example, their behavior can also be tuned to be very hydrophilic and in this case, the fibers will exhibit a very high affinity to water. Such hygroscopic fibers are capable of advantageously eliminating (absorbing) any free water in the lubrication system as well as any dissolved water. If placed in or on a seal, they can act as an active water removal device for industrial lubricants.
As will be further discussed below, one particularly advantageous example of such a system is a sealed bearing wherein the seal is able to adsorb water, which would otherwise be very harmful to the bearing system. Water can result in corrosion and/or hydrolysis of the lubricant, for example, leading to early failures.
Thus, in certain aspects of the present teachings, hydrophilic and/or hygroscopic fibers may be disposed on the surface of a seal in addition or in the alternative to the above-described oleophilic fibers.
Solid Lubricant or Solid Oil
In the past, known “solid oil” products have been made by saturating a polymer matrix with oil. Such solid oils have an oil content of up to 70%, but are much harder than is usual for lubricating greases. Due to the relatively stiff mechanical structure, they can provide more support than greases, while the relatively high oil content provides better lubrication than can be achieved by pure polymer materials.
A fiber-thickened grease can be prepared utilizing oleophilic fibers according to the present teachings such that it has a comparable stiffness to known solid oils and similar materials and therefore has the same functionality. However, in this aspect of the present teachings, performance can also be improved as compared to known solid oils, because the oleophilic fibers themselves can also act as a lubricant, i.e. the oleophilic fibers supplement the lubricating properties of the base oil. For example, in such embodiments, fibrous material may shear off during operation, thereby increasing the gap between the functional surface and the “grease” that reduces friction. If lubricating fibers enter the contact, they can provide additional lubrication.
In addition, by tuning the oleophilic properties of the present fibers, e.g., by coating or treating the fibers, the oil bleeding rate of the resulting grease can be tuned, e.g., for various bearing applications. By making a solid oil using very viscous fiber-thickened grease in accordance with the present teachings, different solid oil products can be easily formulated for different bearing types/operating conditions.
Such solid oils preferably have a hardness values between 1% and 100% of the hardness of the base material of the polymer fibers.
Hydrophilic fibers or fibrous materials according to the present teachings are preferably disposed in fluid communication with the solid oil in order to remove water from the solid oil, e.g., during operation of the lubricant system. Due to the solid-like nature of the solid oil, it may be necessary to arrange a plurality of local deposits of hydrophilic fibers or hydrophilic materials (e.g., fabrics or pads) within the system to provide sufficient hygroscopic functionality.
In another aspect of the present teachings, lubricants are provided in the form thickened oils and greases. More specifically, lubricating fluids or oils preferably may be thickened with oleophilic fibers according to the present teachings. However, it should be understood that the present hydrophilic fibers, and hydrophilic materials made therefrom, may be utilized with a wide variety of lubricants that may be thickened with conventional soap materials or any other known lubricant thickening agents.
According to this aspect of the present teachings, while the most appropriate consistency is often determined by the application or usage of the thickened lubricant, the NLGI grade or consistency (the standard set or determined by the National Lubricating Grease Institute) is preferably equal to or greater than 00. More preferably, lubricants according to the present teachings may have a consistency or NLGI grade between 1 and 3, e.g., 2. Such thickened greases are particularly suitable for usage in bearings.
If loose oleophilic fibers are utilized to thicken the lubricant, the optimal density of the oleophilic fibers in the thickened lubricant will depend on the required viscosity and consistency of the lubricant for the particular application, as well as the length and diameters of the fibers utilized to thicken the lubricating fluid or oil. However, it is noted that preferred oleophilic fiber weight densities (based on the total lubricant weight) for a fiber-thickened lubricant are generally between about 0.1 and 20%. Preferred fiber densities for a fiber-thickened ‘grease’ are generally about 2-15%, more preferably between about 5-12%. But, in case the oleophilic fibers are used in conjunction with other thickeners, the fiber content may be reduced accordingly.
Again, hydrophilic fibers according to the present teachings may be disposed in fluid communication with the thickened lubricant in order to remove water from the base lubricating fluid, e.g., an oil.
Oil separation typically takes place when grease is stored for long periods of time, e.g., in a drum. In this case, the oil becomes visible as an oil layer on top of the grease. In general, the oil is lighter or less dense than the soap or other thickening material, so that the oil will float on the remaining grease. This separation phenomenon governs the “shelf life” of the grease, i.e. the amount of time that the grease may be safely stored before using. Release of oil ‘on the shelf’ is therefore undesirable, and this presents a challenge, because the grease must be capable of bleeding sufficient oil in order to function as a good lubricant during operation. Therefore, shelf life and sufficient bleeding characteristics during usage need to be suitably balanced.
Oleophilic fiber-thickened greases according to the present teachings can be prepared that exhibit a longer shelf life. In particular, two parameters may be controlled to influence the shelf life.
First, progressive structural changes affect the thickener (fiber) structure. These are influenced by the ability of the structure to retain the oil and hence to the affinity between the oil and the structure. A highly oleophilic structure will retain the oil better than an oleophobic structure. Furthermore, the stability of the structure can be optimized as described elsewhere in this specification.
Second, the buoyancy of the thickening material in the oil also affects the shelf life. The thickener can be designed such that the specific mass (density) is almost equal to the specific mass (density) of the oil or lubricating fluid comprised in the grease. In this case, the oil or lubricating fluid is less able to float on top of the remaining grease, because they have equal or substantially equal specific masses.
In addition or in the alternative, the fibers can be coated or treated or thus selected in a manner that will maintain the base oil inside the fiber network (oleophilic properties) for a longer period of time.
The oleophilicity of the fibers can be determined according to a variety of techniques that are known in the surface science field. For example, as was described above, the contact angle of a drop of oil or lubricating fluid on a smooth flat surface of the same material as the fiber may provide one indication of the oleophilicity of the fiber. In this case, the lower or shallower the internal contact angle, the more oleophilic the material is. The oil is said to ‘wet’ the material when the internal contact angle is very shallow. Another method for indicating oleophilicity is to determine the volume of oil that a cloth or other structure (e.g., fabric) made of the fibers can absorb.
Again, hydrophilic fibers according to the present teachings may be disposed in fluid communication with the lubricant in order to remove water during storage of the lubricant, thereby further increasing its shelf life. The fibers may be deposited, e.g., on a wall or other surface of a drum or vat containing the stored lubricant.
A hydrophilic polymer fiber network according to the present teachings can be designed so that it retains solid additive particulates within the fiber network and independently of any treatment performed on the fibers themselves. The size of these particulates can be nano-, micro- or meso-scale. Particulates having a size on the order of tens of microns are known as mesoparticles. In this aspect of the present teachings, the retention of a particulate “additives reservoir” in the fiber network can be provided.
Nano-, micro- and meso-scale particles having anti-wear properties (for example, by admixing non-dissolved zinc dialkyldithiophosphate, ZDDP), anti-friction or friction-reducing properties (for example, by admixing one or more of MoS2, WS2, and/or PTFE), anti-oxidant properties, and/or anti-corrosion properties can be added as ingredients in the “structure forming” (i.e. fiber network making) process. Anti-corrosion additives and preservatives can also be incorporated into the fiber network.
In addition or in the alternative, if the fibers are treated such that certain additives will adhere thereto, a fiber structure will result that incorporates the required additive/chemistry. That is, the required or desired property or properties is/are present in the lubrication system as long the fibers are contained in the lubrication system, e.g., as a network or as a suspension/dispersion (e.g. a paste).
In another aspect of the present teachings, fibers according to the present teachings (e.g., hydrophilic fibers having a length generally between about 50 nm to 10 μm) may be adhered to or incorporated into a seal, seal-lip or seal-lip dual layer, e.g., of a bearing or shaft seal, in order to absorb and remove any water or other hydrophilic substances within the lubricant for the bearing or shaft seal.
The FIGURE shows a representative bearing application of the present teachings. In this exemplary embodiment, a plurality of ball bearings 1 (only one is shown for purposes of clarity) are movably disposed between two rings 2 (i.e. an outer ring and an inner ring) of a bearing. The ball bearings 1 may be guided within respective tracks or raceways defined in the rings 2. Seals 3 may be disposed on opposite axial ends of the bearing in order to define a closed or sealed space within the bearing for retaining a lubricant, such as a grease suitable for bearing applications.
The seals 3 may be made from rubbers and or elastomeric polymers, e.g., nitrile rubber (NBR) and polyurethane (PU) materials, and can be produced according to any suitable technique known in the art. Other materials can, in principle, be used as well.
The seals 3 optionally may be porous so as to define oil reservoirs in the surface thereof. One representative example for making such porous seals 3 is to add salts, such as NaCl or CaCO3, to the elastomer mixture prior to molding. After molding the seal, the salts are washed out of the seal lip using an aqueous solution, thereby creating pores in the surface that are capable of absorbing, retaining and/or storing oil during operation of the seal.
In a preferred embodiment, an oil-swollen porous network may then be produced by adhering an oleophilic nano or micro-porous fiber network according to the present teachings to the seal material, e.g., to the above-mentioned pores. The adhesion is preferably strong enough to provide sufficient wear resistance. This can be achieved by using appropriate adhesion chemistry as is well known in the art. This porous network can also be adhered to a seal counterface (opposing) surface.
In another embodiment, a thicker ‘pad’ -like structure comprising fibers according to the present teachings (e.g., a cloth, fabric, pad, mat, etc., as was discussed above) may be adhered to the seal or onto a counterface surface.
In another embodiment, a heterogeneous mixture of oil-swollen fibrous networks and commonly-used seal materials can be utilized to incorporate pockets of oil-swollen structures into the seal (or counterface) structure.
As the oil reservoir(s) is (are) only needed near the seal lip, the surface layer (liner) may be porous and may be combined with a standard seal material (such as NBR). If the two materials are the same (e.g., both NBR or PU), they can be more readily bonded together during the cross-linking step. This prevents adhesion problems in the bonding layer that might arise when friction forces apply stress to this layer.
One or more hydrophilic materials 4 according to the present teachings may be disposed, preferably in fluid communication with the lubricant within the sealed space defined, in part, by the seals 3. For example, a hydrophilic pad 4 may be disposed, e.g., adhered, to a portion of one or both rings 2 of the bearing that do(es) not contact the ball bearings 1, to a radially-extending, interior portion of the seal 3 or to a non-contacting side of the sealing lip. The hydrophilic materials 4 may also be disposed outside of the sealed space, such as a radially-extending, exterior portion of the seal 3.
In this way, the hydrophilic material 4 is in fluid communication with the lubricant, e.g., grease, and can effectively remove water and/or other hydrophilic substances during storage and/or operation of the bearing.
Naturally, the present teachings are not limited to ball bearings, but may be utilized with any type of bearings, including but not limited to cylindrical bearings, tapered bearings, spherical bearings, etc.
Moreover, the present teachings are generally applicable to any type of system or device that utilizes a lubricant, which may become contaminated with water or other hydrophilic substances either during storage or operation, including but not limited to rotatable shafts and shaft seals, gear boxes, linear actuators, etc.
Hydrophilic Fibers Applied to a Surface Utilizing a Melt-Spinning Process
In the alternative to adhering a fibrous material, e.g., a pad or fabric, to a surface that is in fluid communication with the lubricant, a melt-spinning process can be used to directly apply hydrophilic fibers according to the present teachings onto the surface of a metallic conductor, thereby leading to in situ deposition and a very cost-effective way of using the hydrophilic fibers. The fibers may be sprayed directly onto the bearing ring or seal surfaces in the production line and then allowed to cool. This manufacturing step could be performed in various ways, e.g., by controlling both the speed of spraying and rotating the target surfaces. This process will result in a fiber coating on the surface that will adsorb water. In one embodiment, the fibers are produced using melt-blowing techniques that directly apply the fibers onto the target object. In an alternative embodiment, electro-spinning processes can be utilized for very accurate fiber production and deposition control onto the metallic objects.
In one embodiment thereof, the fibers may function as a preservative (corrosion-preventing substance) for the bearing. The hydrophilic fibers (e.g., applied according the above-described spray-on method) may be used to remove water from the lubricating system.
The same applies for conductive seals according to the preceding embodiments.
If the seal polymers are not conductive, another option is to use the super cooling effect so that overmolding is possible.
Another aspect of the present teachings concerns embodiments, which enable oil to be pumped or moved within the lubrication system, but wherein the moving parts are lubricated with greases, such as in a gearbox.
In one embodiment of this aspect of the present teachings, oleophilic polymer fiber thickeners and oils may be sprayed inside bearings separately in order to form a self-generating grease inside the bearing. For this purpose, polymer fibers may be processed, e.g., into granules or particles. Oils may then be subsequently sprayed into the bearing separately, e.g., as a fine oil mist. The oil and polymer fiber particles will then (re)combine in situ to form a grease.
In another embodiment, the fibers may be produced, e.g., by melt-blowing or electro-spinning, and then deposited onto the surface of gears, gearboxes, bearings, etc. The oil is added separately or just before application to the mechanical system.
One advantage of this embodiment is that pumping of oil is easier (less energy intensive) than pumping of thick grease, because oil is less viscous. Thus, energy consumption may be reduced without sacrificing lubricating performance.
Another advantage of this embodiment is that the distribution of grease inside the bearing, e.g., on the cage, or in the rolling contact, can be fully controlled.
Another advantage is the complete freedom and variability of grease formulation depending on re-lubrication needs and operating conditions.
Another advantage is that the bearing may be lubricated with oil to ensure replenishment of the rolling contact, wherein excess oil is adsorbed in the shape and form of grease.
Another advantage is that the hydrophilic material may be disposed at a wider variety of locations within the lubricating system. For example, the hydrophilic material may optionally be disposed near a pump or filter and need not be physically located within the device in need of lubrication.
In any of the above-mentioned embodiments, in which fibers are deposited onto (e.g., adhered to, embedded or incorporated in, etc.) a surface that is in fluid communication with the lubricant, the thickness of the fibers may be between one monolayer of fibers (or fabric material) to tens of layers up to hundreds of layers. Particularly preferred ranges are between 1-50 layers, more preferably 2-20 layers.
Additional embodiments of the present teachings disclosed herein include, but are not limited to:
1. A grease comprising an oil and/or lubricating fluid and thickening fibers having a length in the micron range and a diameter or width in the micron or nanometer range, the fibers being oleophilic.
2. A grease according to embodiment 1, wherein the fibers comprise at least two portions having different physical and/or chemical properties.
3. A grease according to embodiment 2, wherein at least one of the portions has a higher affinity to a like portion than to the oil and/or lubricating fluid, thereby imparting a self-assembly property to the thickening fibers.
4. A grease according to any preceding embodiment, wherein the fibers have a length of 100-500 microns.
5. A grease according to embodiment 4, further comprising oleophilic thickening fibers having a length of 1-100 microns.
6. A grease according to any one of embodiments 1-3, wherein the fibers have a length of 1-100 microns.
7. A grease according to any preceding embodiment, wherein the fibers have a length that is at least about 5-10 times the diameter thereof.
8. A grease according to any preceding embodiment, wherein the thickening fibers are a mixture of organic fibers, e.g., polypropylene, and inorganic, e.g., ceramics, e.g., aluminum oxide and/or silicon dioxide.
9. A grease according to any preceding embodiment, wherein the fibers also have oleophobic and/or hydrophilic properties.
10. A grease according to any preceding embodiment, further comprising non-oleophilic fibers having oleophobic and/or hydrophilic and/or hygroscopic properties.
11. A grease according to any preceding embodiment, wherein the fibers are biodegradable.
12. A grease according to any preceding embodiment, wherein the thickening fibers comprise cellulose and/or gum.
13. A grease according to any preceding embodiment, wherein the thickening fibers are coated, e.g., randomly coated, with a composition that is more polar than the thickening fiber.
14. A grease according to any preceding embodiment, wherein the thickening fibers comprise Janus fibers.
15. A grease according to any preceding embodiment, wherein the thickening fibers are comprised of a mixture of at least one polar polymer, e.g., polyethylene oxide (PEO), and at least one non-polar polymer, such as polystyrene (PS) or polypropylene (PP).
16. A grease according to embodiment 15, wherein the fiber is a block co-polymer.
17. A grease according to any preceding embodiment, wherein the fibers have a strong affinity for steel and/or polymer surfaces.
18. A grease according to any preceding embodiment, wherein the fibers form a sponge-like network that absorbs or retains the lubricating fluid or oil.
19. A grease according to embodiment 18, wherein the sponge-like network has the property that it shrinks or contracts as the temperature increases, thereby squeezing out lubricating fluid or oil.
20. A grease according to any preceding embodiment, wherein the grease comprises at least two types of thickening fibers, each having a different melting temperature.
21. A grease according to embodiment 20, wherein at least the thickening fiber having the lowest melting temperature acts as a lubricant when the grease is brought to a temperature above the melting temperature of said thickening fiber.
22. A grease according to any preceding embodiment, wherein the thickening fibers are formed from a wax and/or further comprising wax.
23. A grease according to any preceding embodiment, further comprising a low molecular weight polymer, e.g., a wax, that cross-links thickening fibers having a higher molecular weight.
24. A grease according to embodiment 22 or 23, wherein the wax is a natural wax or a hydrocarbon wax.
25. A grease according to embodiment 24, wherein the wax is bees wax or paraffin wax.
26. A grease according to any preceding embodiment, wherein the thickening fiber is a tackifier or further comprising a tackifier.
27. A grease according to any preceding embodiment, wherein the thickening fibers and the lubricating fluid or oil are selected such that the thickening fibers are capable of self-generating a fibrous sponge-like network when the thickening fibers contact the lubricating fluid or oil.
28. A fiber according to any preceding embodiment (i.e. without the oil or lubricating fluid), preferably constituting between about 0.1 and 100 wt % of a final material, more preferably about 50-100 wt %.
29. A bearing surface coated with a fiber according to embodiment 28 or having a fiber according to embodiment 28 embedded or incorporated into the bearing surface, the bearing surface preferably comprising steel.
30. A seal coated with a fiber according to embodiment 28 or having a fiber according to embodiment 28 embedded or incorporated into the surface of the seal, the seal optionally comprising an elastomeric material, e.g., NBR or polyurethane and/or wax fibers disposed in the seal.
31. A bearing cage coated with a fiber according to embodiment 28 or having a fiber according to embodiment 28 embedded or incorporated into the surface of the cage, the cage preferably comprising steel or polyamide.
32. A bearing surface or seal or bearing cage according to embodiments 29-31, respectively, having a plurality of oil reservoirs defined in the bearing surface or seal surface or cage surface, respectively, the fibers and oil reservoirs being located at least a primary point of contact between two parts moving relative to each other during operation.
33. A bearing surface or seal or bearing cage according to embodiments 29-31, respectively, having a porous surface structure and/or a surface structure that has been chemically treated to cause lubricating fluid or oil to be released from the grease under prescribed operating conditions.
34. A grease, fiber, seal or bearing cage according to any preceding embodiment, wherein the oleophilic thickening fibers have a diameter between about 50 nm and 10 microns, and more preferably between about 100 nm and 1 micron.
35. A grease, fiber, seal or bearing cage according to any preceding embodiment, wherein the oil and/or lubricating fluid comprises one or more of mineral oil obtained from crude oil, group I, II and III lubricants, group IV lubricants (polyalphaolefins “PAO”) and group V lubricants (all others).
36. A grease, fiber, seal or bearing cage according to any preceding embodiment, wherein the oil and/or lubricating fluid comprises one or more of mineral oil, synthetic ester, and plant-based oil and their derivatives, such as oils derived from rapeseed, canola, sunflower, canola and palm.
37. A grease, fiber, seal or bearing cage according to any preceding embodiment, wherein the oil and/or lubricating fluid comprises one or more of animal-based oils, their derivatives and synthetic lubricants such as polyglycols (PG), polyalkylene glycol (PAG), white oils, silicone oils, very-high viscosity index oils (VHVI), water, glycerol and waxes.
38. A grease, fiber, seal or bearing cage according to any preceding embodiment, wherein the oil and/or lubricating fluid has a viscosity that is between about 1-1000 cSt at 40° C.
39. A grease, fiber, seal or bearing cage according to any preceding embodiment, wherein the fibers comprise a polymeric material that has been spun into fibers.
40. A grease, fiber, seal or bearing cage according to any preceding embodiment, wherein the fibers comprise one or more of polyamide (PA), nylon 6,6, polyamide-6,6 (PA-6,6), polyamide-4,6 (PA-4,6), polyurethanes (PU), polybenzimidazole (PBI), polycarbonate (PC), polyacrylinitrile (PAN), acrylonitrile rubber (NBR), polyvinylalcohol (PVA), polylactic acid (PLA), polyethylene-co-vinyl-acetate (PEVA), PEVA, polymethacryate (PMMA), tetrahydroperfluorooctylacrylate (TAN), polyethylene oxide (PEO), collagen-PEO, polyaniline (PANI), polystyrene (PS), silk-like polymer with fibronectin functionality, polyninylcarbazole, polyethylene rerephtalate (PET), polyacrylic acid (PAA), polypyrene methanol (PM), polyvinylphenol (PVP), polyvinylchloride (PVC), cellulose acetate (CA), polyacrylamide (PAAm), PLGA, collagen, polycaprolactone (PCL), poly(2-hydroxyethyl methacrylate) (HEMA), poly(vinylidene fluoride) (PVDF), polyether imide (PEI), polyethylene glycol (PEG), poly(ferrocenyldimethylsilane) (PFDMS), poly(ethylene-co-vinyl alcohol), polyvinyl pyrrolidone (PVP), polymetha-phenylene isophthalamide, polypropylene (PP), polyethylene naphthalate (PEN), Teflon®, polytetrafluorethene (PTFE), waxes, waxy polymers, polyolefins, polyesters, and polysulfones.
41. A grease, fiber, seal or bearing cage according to any preceding embodiment, wherein the fiber comprises one or more polymers derived from a natural or biodegradable source, such as, e.g., polysaccharides, such as cellulose, starch, chitin, chitosan, proteins, (poly)peptides and gelatin.
The preferred embodiments and exemplary examples were described above in combinations of features and steps that may not be necessary to practice the invention in the broadest sense, and such detailed combinations have been described merely for the purpose of particularly describing representative examples of the invention. Furthermore, various features of the above-described representative examples, as well as the various independent and dependent claims, may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings.
All features, oils, base lubricating fluids, materials, polymers, fibers, additives, etc. disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter, independent of the compositions of the features in the embodiments and/or the claims.
In addition, all value ranges or indications of groups of entities are intended to disclose every possible intermediate value or intermediate entity for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter.
The present application claims priority to US provisional application no. 61/406,416 filed on Oct. 25, 2010, U.S. provisional application no. 61/418,081 filed on Nov. 30, 2010, U.S. provisional application no. 61/421,985 filed on Dec. 10, 2010 and U.S. provisional application no. 61/426,083 filed on Dec. 22, 2010, the contents of all of which are incorporated by reference as if fully set forth herein.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP11/68679 | 10/25/2011 | WO | 00 | 6/20/2013 |
| Number | Date | Country | |
|---|---|---|---|
| 61406416 | Oct 2010 | US | |
| 61418081 | Nov 2010 | US | |
| 61421985 | Dec 2010 | US | |
| 61426083 | Dec 2010 | US |
